#head_line{
    border: 1px solid red;
    height: 70px;
}
#head_mid_title{
    border: 1px solid black;
    height: 160px;
}
.li_free{
    position: relative;
    display: inline-block;
    width: 210px;
    height: 230px;
    border: 1px solid blue;
    margin: 10px;
}
img{
    position: absolute;
    width: 210px;
    height: 130px;
}
.course_title{
    position: absolute;
    top: 130px;
    left: 8px;
    
}
.free{
    position: absolute;
    top: 195px;
    left: 15px;
    color: #75a5fe;
    
}
.enroll{
    position: absolute;
    top: 195px;
    left: 125px;
    color: #939696;
    
}